Labyrinth seal

ABSTRACT

A labyrinth seal including a stator and a non-contacting rotor, and annular elastomeric seals. The confronting surfaces of the stator and rotor define at least one interface passage, including a radially-outermost annular interface passage between an annular, outermost, radially-extending projection of the stator and an annular rearwardly-extending distal projection of the rotor that overlaps the radially-extending projection of the stator, the radially-outermost annular interface passage tapering outwardly and rearwardly at an acute angle relative to an axial reference line. The annular elastomeric seals are stationary with the stator during dynamic operation of the rotor, and are not contacted by a surface of the rotor during dynamic operation. The interface can also have two radially-disposed exclusion chambers, the outer exclusion chamber being defined in part by a radially-inboard projection of the rotor. The stator can have a projection providing a contact avoidance interface position inboard of at least two contaminant-excluding interfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/455,162, filed Aug. 8, 2014, which is a continuation-in-partapplication of PCT International Application PCT/US2013/025505, filedFeb. 11, 2013, which claims the benefit of U.S. provisional application61/597,587, filed Feb. 10, 2012, the disclosures of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to a shaft-sealing and bearingprotecting labyrinth seal for a shaft-driven rotating equipment.

BACKGROUND OF THE INVENTION

Adequate maintenance of rotating equipment is difficult to obtainbecause of extreme equipment duty cycles, the lessening of servicefactors, design and the lack of spare rotating equipment in manyprocessing plants. This is especially true of process pumps, slurrypumps, machine tool spindles, wet end paper machine rolls, aluminumrolling mills and steam quench pumps and other equipment utilizingextreme contamination that can affect lubrication of the bearings of therotating equipment.

Various forms of shaft sealing devices have been utilized to try toprotect the integrity of the bearing environment, including rubber lipseals, clearance labyrinth seals, and attraction magnetic seals. Lipseals or O-ring shaft seals can quickly wear out and fail and are alsoknown to permit excessive amounts of moisture and other contaminants tomigrate into the lubricant (oil or grease) reservoir of the operatingequipment even before failure had the interface between the rotor andthe stator exposed to the contaminates or lubricants at the radialextremity of the seal.

Labyrinth-type seals involving closely related stator and rotor rings,which do not contact each other but define labyrinth passages betweenthem have been devised and utilized and are illustrated in U.S. Pat.Nos. 4,706,968, 4,989,883, 5,069,461, and 6,419,233, the disclosures ofwhich are incorporated by reference in their entireties.

SUMMARY OF THE INVENTION

The present invention provides an improvement to labyrinth seals forprotecting bearings from lubricant leakage, and entry of liquid andvapor contaminants.

The present invention relates to an improvement to a labyrinth sealhaving a stator and a rotor, and one or more annular elastomeric sealsdisposed between the confronting surfaces of the stator and rotor.

An aspect of the present invention is a labyrinth seal having aradially-outermost annular interface between the stator and the rotorthat defines the initial entry point of liquid or vapor contaminant intothe seal. The entrance into and pathway along the interface is directedradially inwardly to promote expulsion of contaminant that encroachesinto the interface during dynamic operation of the seal.

Another aspect of the present invention is a labyrinth seal including atleast one annular elastomeric seal that is associated with, andstationary with, the stator during dynamic operation of the rotor, andis not contacted by a surface of the rotor during dynamic operation ofthe rotor.

Another aspect of the present invention is a labyrinth seal with aninterface pattern between the confronting surfaces of the stator androtor that define two radially-disposed exclusion chambers, including aradially-outside exclusion chamber and a radially-inside exclusionchamber, to enhance sealing performance.

Another aspect of the present invention is a labyrinth seal withradially-most exclusion chamber defined in part by a radially-inboardprojection of the rotor, for expelling contaminant liquid outwardradially, to enhance sealing performance.

Another aspect of the present invention is a labyrinth seal including acontact avoidance interface between the stator and the rotor that ispositioned in an intermediate portion of the labyrinth pathway, that isinboard of at least two contaminant-excluding interfaces and at leastone lubricant-excluding interface. This feature ensures that any wearassociated with dynamic contact of the rotor with the stator does notdamage the important excluding interfaces.

Another aspect of the present invention is a labyrinth seal with alubricant-contacted surface of the stator having a lubricant collectinggroove having a tapered surface that improves the flow of lubricantthrough a drain in the bottom of the stator, back to the lubricationsump of the rotating equipment.

The present invention also relates to a labyrinth seal including astator and a non-contacting rotor, and including one or more annularelastomeric seals, and at least one interface passage disposed betweenthe confronting surfaces of the stator and rotor, the at least oneinterface passage including a radially-outermost annular interfacepassage between an annular, outermost, radially-extending projection ofthe stator and an annular rearwardly-extending distal projection of therotor that includes an annular inner surface that overlaps theradially-extending projection of the stator, the radially-outermostannular interface passage tapering outwardly and rearwardly at an acuteangle relative to an axial reference line.

The present invention also relates to a labyrinth seal including astator and a non-contacting rotor, and including at least one annularelastomeric seal, wherein the at least one annular elastomeric seal isstationary with the stator, and is not contacted by a surface of therotor during dynamic operation.

The present invention further relates to a labyrinth seal including astator and a non-contacting rotor, and including at least one annularelastomeric seal, wherein the confronting surfaces of the stator androtor define two radially-disposed exclusion chambers including aradially-outer exclusion chamber and a radially-inner exclusion chamber.

The present invention further relates to a labyrinth seal including astator and a non-contacting rotor, and including at least one annularelastomeric seal, further including a contact avoidance interfacedisposed in an intermediate portion of the labyrinth pathway between thestator and the rotor, that is inboard of at least twocontaminant-excluding interfaces and at least one lubricant-excludinginterface, that provides a first interface of contact between theconfronting surfaces of the stator and rotor in the event the rotormoves axially toward the stator during dynamic operation of the seal.

The present invention further relates to a labyrinth seal including astator and a non-contacting rotor, and including at least one annularelastomeric seal, wherein the confronting surfaces of the stator androtor define a radially-outside exclusion chamber that is defined inpart by a radially-inboard projection of the rotor, for expellingcontaminant liquid outward radially during dynamic operation, to enhancesealing performance.

The present invention also relates to a labyrinth seal including astator and a non-contacting rotor, and including at least one annularelastomeric seal, wherein the stator has a lubricant collecting groovehaving a tapered surface that improves the flow of lubricant through adrain in the bottom of the stator.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be more clearly understood from the followingdetailed description of representative embodiments thereof read inconjunction with the accompanying drawings that form a part of thisdisclosure.

FIGS. 1a and 1b show perspective views of the inner face and outer face,respectively, of the rotor.

FIGS. 2a and 2b show perspective views of the outer face and inner face,respectively, of the stator.

FIG. 3 shows a cross-sectional view of the rotor separated from thestator.

FIG. 4 shows a cross-sectional view of the rotor engaged with the statoron a shaft.

FIG. 5 shows a sectional view of the bottom portions of the rotorseparated from the stator.

FIG. 6 shows a split configuration of the rotor and the stator.

FIGS. 7a and 7b show perspective views of the outer face and inner face,respectively, of an alternative stator.

FIG. 8 shows a cross-sectional view of the rotor separated from thestator of FIGS. 2a and 2 b.

FIG. 9 shows a cross-sectional view of the rotor engaged with the statorof FIG. 8 on a shaft.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1a, 1b and 3-5 show a rotor 1 that includes a forward-facingannular wall 2 extending radially from an inner diameter (ID) edgeproximate the shaft 90 to an outer diameter (OD) edge, and a firstdistal annular projection 4 extending rearwardly from the forward wall 2to a distal end 6. The annular distal projection 4 has an inner annularsurface 8 that tapers outwardly and rearwardly at angle θ relative tothe axial reference line. The inner annular surface 8 is typically amachined, frustoconical-shaped surface having an acute angle θ of atleast 1°, more typically at least 2°, moreso typically at least 3°, andup to 45°, typically up to 15°, more typically up to 10°, and moresotypically up to 5°.

A second intermediate annular projection 10 extends to a distal end 12having a surface substantially perpendicular to an axial reference line100, and has an inner annular surface 13 that extends substantiallyparallel to the axial reference line 100. The second intermediateprojection 10 with the distal projection 4 define a channel surface 9therebetween.

A third proximal annular projection 14 extends rearwardly to a distalend 16. The third proximal projection 14 has at least one first annulargroove 18 formed in the inner surface of the third projection 14proximate the forward wall 2 for retaining a corresponding firstelastomeric seal 80, which seals the annular interface between the rotor1 and the shaft 90. The elastomeric seal 80 is compressed on theequipment shaft and seals any external contaminants from encroachingalong the equipment shaft 90 and into the rotating equipment, and alsoprevents oil or grease lubricant within the rotating equipment fromexiting along the shaft 90 to atmosphere. The elastomeric seal(s) 80grips to the shaft 90 to drive the rotor during dynamic operation of theequipment.

A first annular shoulder 20 is formed in the inner surface of the thirdprojection 14, axially rearward from the first annular groove 18, and asecond annular shoulder 22 is formed in the inner surface rearwardlyfrom the second annular shoulder 22, which defines the end 16. Thedistal end 16 has a surface substantially perpendicular to the axialreference line 100. The third projection 14 with the second intermediateprojection 10 define a channel surface 15 therebetween.

FIGS. 2a, 2b , and 3-5 show a stator 31 that includes an annular body 34having a rearward-facing annular face 32, having a wall 42 with aninner-diameter annular surface 33 proximate the shaft 90, and anouter-diameter annular surface 62 that is configured for press-fitinsertion into a cylindrical bore in the interior of the housing H ofthe equipment. The press-fit interface of the OD annular surface 62provides a primary sealing of the stator within the housing. An annulargroove 64 formed into the OD annular surface 62 can receive an optionalsealant as a secondary sealant to prevent leakage of lubricant along thesurface 62.

A deep, annular groove 36 formed into the inner surface 33 of the body34 proximate to the rear face 32, defines a tapered forward wall 58,providing a lubricant return groove. The tapering of the forward wall 58improves the rate of return of the lubricant down to the drain 89 andback to the sump of the rotating equipment.

The outer annular surface 62 of the stator 31 extends axially forward toa stop shoulder 66 that defines a stop when the stator 31 is insertedaxially into the receiving bore of the housing H of the rotatingequipment, as shown in FIG. 4. The machined stop shoulder 66 alsosquares up the stator with the housing to ensure proper alignment withthe shaft 90.

Axially- and radially-extending projections extend from, and grooves areformed into, the body 34 to form interfacing surfaces and definecavities with the confronting face of the rotor. The wall 42 extendsforward axially from the distal end of radial wall 40 to define aforward-facing annular groove 37 (FIG. 3). A first annular coalescingseal ring 81 is disposed within an annular cavity defined by the groove37 of the stator 31 and the groove 22 formed in the rearward (axially)portion of the third projection 14 of the rotor 1. The first annularcoalescing seal ring 81 is associated with the stator 31, and does notmove or rotate normally (that is, it remains stationary) during dynamicoperation of the rotor 1. During dynamic operation, the rotating rotordoes not touch or contact the first coalescing seal ring 81. A secondannular coalescing seal ring 82 is disposed at least partially within asecond annular groove 56 formed radially into the body 34 of the stator.The second annular coalescing seal ring 82 also remains stationaryduring dynamic operation of the rotor 1. The second coalescing seal ring82 disposed within groove 56 of the stator 31 is also not touched orcontacted by the extending end portion 16 of the third projection 14,including when the rotor 1 and shaft 90 are rotating at operating speed.

A catch 28, with a shoulder 27 and a tapered leading edge 29, extendsradially from the end 16 the third projection 14, to provide a means forlocking the rotor 1 in operational association with the stator 31, aswill be described later.

A forward portion 44 extends both radially and axially from the statorbody 34, and includes an annular, outermost, radially-extendingprojection 46 with a tapered, machined distal edge 48. The distal edge48 is typically a frustoconical-shaped surface having the acute angle θrelative to the axial reference line 100. A second run-off shoulder 68is machined axially rearward of the projection 46 to define a channelbetween the housing H and the distal-most portions of the stator-rotor,to assisting in running off the contaminant liquid away from an entranceinto the labyrinth seal.

When the rotor 1 is operationally associated with the stator 31, themachined distal edge 48 defines a tapered annular interface passage 70with the inner surface 8 of the rotor's distal projection 4 thatoverlaps the outermost distal edge of the stator. This tapered interfacepassage defines the initial entry point of a liquid contaminant into theseal between the distal edge of the rotating rotor and the stationarystator. The entrance into and pathway along the interface passage isdirected radially inwardly to promote expulsion of contaminant thatencroaches into the interface during dynamic operation of the seal.

The forward portion 44 of the stator body 34 also includes a projection50 with a machined distal end 52, which extends forward axially from themachined radial surface 53. The surface of the distal end 52 and thesurface of the machined distal end 52 are substantially perpendicularwith the axial reference line 100. When the rotor 1 is operationallyassociated with the stator 31, the machined distal end 12 of theintermediate projection 10 of the rotor 1 forms a second radialinterface passage 72 with the axial surface 53 of the stator, while thedistal end 52 of the projection 50 of the stator 31 forms a third radialinterface passage 74 with the machined inner surface 15 of the rotor. Inaddition, the annular inner surface of the intermediate projection 10confronts and forms a fourth axial interface passage 76 with the annularouter surface of the projection 50.

The projections and grooves of the confronting rotor and stator define afirst, outer radially-extending exclusion chamber 24 defined by thedistal projection 4, the channel surface 9, and the intermediateprojection 10 of the rotor 1, which are rotating during dynamicoperation, and the axial surface 53 of the stator 31, which isstationary. The outer exclusion chamber 24 is in fluid communicationwith the tapered interface passage 70 and the second axial interfacepassage 72. During operation, any liquid contaminant that passes throughthe tapered interface passage 70 and into the outer exclusion chamber 24will be struck and flung outward radially by the rotating intermediateprojection 10.

A second, inner exclusion chamber 26 is defined by the projection 50 andforward portion 44 of the stator 31, which are stationary during dynamicoperation, and the third projection 14 and the channel surface 15 of therotor 1, which is rotating. The second, inner exclusion chamber 26 is influid communication with the third interface passage 74.

An optional annular contaminant collection groove 54 is formed into theinner surface of the forward portion 44 of the stator 31 that isdesigned to collect any contaminant liquid which might get through theinterface passages 70, 72, 74 and 76, before reaching the second annularcoalescing and retainer seal ring 82. The outer exclusion chamber 24 andinner exclusion chamber 26 provide a pair of radially-disposed exclusionchambers that enhance sealing performance. A virtual radial planeperpendicular to the axial reference line 100 can pass through a portionof both the outer exclusion chamber 24 and inner exclusion chamber 26.

The labyrinth seal also includes a means for locking the rotor 1 to thestator 31 after assembly to prevent axial separation of the rotor 1 fromthe stator 31. Catch 28 and sealing and retainer ring 82 provide alocking means that prevents axial separation of the rotor from thestator when axial adjustments on certain centrifugal process pumps aremade or other axial movements or alignments of the shaft are required.The annular groove 56 in the stator body 34 is formed with a widthessentially that of the cross-sectional diameter of the sealing member82, and is formed to a radial depth less than, and typically aboutone-half, the diameter of the sealing and retainer ring 82. To obtainthe locking action, the sealing and retainer ring 82 is inserted withinthe groove 56 and the stator inserted onto the shaft 90 and within thehousing. As the rotor is pressed into assembly with the stator, theelastomeric sealing and retainer ring 82 is deformed by the leadingbeveled surface 29 of the catch 28, and forced up into the groove 56until the catch 28 clears past the groove 56, which allows the sealingand retainer ring 82 to expand to its natural shape behind the shoulder27 of the catch 29. Once in the locked position, the sealing andretainer ring 82 blocks relative axial movement of the rotor away fromthe stator, unless excessive axial force is applies to the rotor thatcauses the shoulder 27 of the catch to shear through the elastomericmaterial of the seal 82. Further details of such a locking mechanism aredescribed in U.S. Pat. No. 5,378,000, the disclosure of which isincorporated by reference in its entirety.

The stator 31 is designed and configured to prevent migration oflubricant into the labyrinth seal, and to efficiently return thelubricant to the sump of the equipment. Typically the viscosity of thelubricant prevents migration into the narrow interface passages of thelabyrinth seal. Any lubricant that may migrate along interface passagebetween the shaft 90 and the lateral wall 42 confronts the machinedinterface 79 between the end 43 of the lateral wall 42 of the stator andthe inner shoulder 20 of the proximal projection 14 of the rotor, andpasses through axial interface 78, before arriving at the coalescingseal 81 disposed within the annular cavity formed by the groove 37 ofthe stator 31 and the groove 22 of the proximal projection 14.

The device includes a contact avoidance interface between the stator andthe rotor that is positioned in an intermediate portion of the labyrinthpathway. The purpose of the contact avoidance interface is to provide afirst interface of contact of the rotor with the stationary stator, inthe event that the rotor, though fixed to the shaft 90, moves axiallytoward the stator during dynamic operation. Preferably, the contactavoidance interface is disposed inboard in the labyrinth seal pathway,and typically inboard of at least two contaminant-excluding interfaces,for example interface 70 and 72, and inboard of at least onelubricant-excluding interface, for example, interface 79 or coalescingseal 81. This feature provides a dedicated surface for any contact andwear associated with dynamic contact of the rotor with the stator, andprevents the projection members and surfaces forming the other sealinginterfaces, such as interfaces 70 and 72, from making contact duringdynamic operation of the seal, thereby avoiding wear and damage to theinterfaces and maintaining exclusion performance of the seal. In theillustrated embodiment shown in the Figures, the contact avoidanceinterface consists of third axial interface passage 74 defined betweenthe distal end 52 of the projection 50 of the stator 31, and themachined inner surface of forward wall 2 of the rotor. The end 52 ofprojection 50 is machined to a dimension so that it first contacts theinner surface of forward wall 2 of the rotor when the rotor movesaxially toward the stator. Alternatively, the contact avoidanceinterface may consist of an axial projection of the rotor, and acomplementary surface of the stator.

A bottom portion of the forward portion 44 of the stator body 34 of thestator 31 is removed by well known means to provide a contaminant drain88, as shown in FIGS. 2a and 2b . Any contaminant liquid, such aswashing water dispensed from high-pressure hoses during routine cleanup,or other liquids or vapors in the environment that pass through or tothe interface passages 70, 72, 74 and 76, and collects in the annularouter chamber 24 and inner chamber 26, or in the annular groove 54,passes downward and drains from the drain 88. The annular distalprojection 4 that extends entirely around the circumference of therotor, as shown in FIG. 4, has a downwardly-sloping surface 8 at thebottom helps to drain contaminant liquid out from the seal. Theinterface gaps 70, 72, 74 and 76 are preferably machined to a hightolerance and narrowest spacing possible.

FIG. 6 shows another embodiment of the rotor and stator in a splitconfiguration, which allows the seal to be installed on an equipmentshaft in place, without needing to slip the rotor or stator over the endof the shaft 90. The rotor includes opposed and substantially identicalupper rotor portion 1 a and lower rotor portion 1 b, each including athreaded bore 91 and a through bore 92 formed in the opposed portions ofthe rotor body, which receive threaded fasteners 93 for securing theportions 1 a and 1 b to the shaft 90. The stator includes opposed upperstator portion 31 a that has two opposed through bores 92, and lowerstator portion 31 b that has two opposed threaded bores 91, forreceiving threaded fasteners 93 for securing the portions 31 a and 31 bto the shaft 90. Lengths of o-ring cord stock 85 are placed into therespective grooves in the upper rotor 1 a and lower rotor 1 b, and upperstator 31 a and lower stator 31 b portions, to form the elastomeric sealmembers.

FIGS. 7a, 7b , 8 and 9 show a stator 131, similar to the aforementionedstator 31 shown in FIGS. 2a and 2b , with common features illustratedand numbers the same. Similar to the above embodiment, the bottomportion of the forward portion 44 of the stator body 34 of the stator131 is removed by well known means to provide a contaminant drain 188,as shown in FIGS. 7a and 7b . Unlike the embodiment illustrated in FIGS.2a and 2b , the containment drain 188 does not remove any portion of theannular stop shoulder 66.

It is understood that modifications to the invention may be made asmight occur to one with skill in the field of the invention within thescope of the appended claims. All embodiments contemplated hereunderthat achieve the benefits of the invention have therefore not been shownin complete detail. Other embodiments may be developed without departingfrom the spirit of the invention or from the scope of the appendedclaims.

We claim:
 1. A labyrinth seal including a stator and a non-contactingrotor, and including at least one annular elastomeric seal, whereinconfronting surfaces of the stator and rotor define a radially-outsideexclusion chamber with a substantially rectangular cross-section boundedby a first radially-extending annular surface of the rotor, a firstradially-extending annular surface of the stator spaced axially from thefirst radially-extending annular surface of the rotor, an annularrearwardly-extending distal projection of the rotor, and an annularrearwardly-extending, radially-inboard intermediate projection of therotor, wherein an axial width of the radially outside exclusion chamberis defined by the axial thickness of the annular rearwardly-extending,radially-inboard intermediate projection of the rotor.
 2. The labyrinthseal according to claim 1, further having a radially-outermost annularinterface passage between an annular, outermost, radially-extendingprojection of the stator and the annular rearwardly-extending distalprojection of the rotor that includes an annular inner surface thatfaces radially inwardly and overlaps the outermost, radially-extendingprojection of the stator.
 3. The labyrinth seal according to claim 1,wherein the at least one annular elastomeric seal is disposed in anintermediate portion of an interface passage between the confrontingsurfaces of the stator and rotor, is stationary with the stator duringdynamic operation of the rotor, and is not contacted by a surface of therotor during dynamic operation.
 4. The labyrinth seal according to claim1, further including a contact avoidance interface disposed in anintermediate portion of a labyrinth pathway between the stator and therotor, that is inboard of at least two contaminant-excluding interfacesand at least one lubricant-excluding interface, that provides a firstinterface of contact between the confronting surfaces of the stator androtor in the event the rotor moves axially toward the stator duringdynamic operation of the seal.
 5. The labyrinth seal according to claim1, wherein a contact avoidance interface comprises an axial projectionof the stator.
 6. The labyrinth seal according to claim 1, wherein thestator has a lubricant collecting groove having a tapered surface thatimproves the flow of lubricant through a drain in a bottom of thestator.
 7. The labyrinth seal according to claim 2, further including acontact avoidance interface disposed in an intermediate portion of alabyrinth pathway between the stator and the rotor, that is inboard ofat least two contaminant-excluding interfaces and at least onelubricant-excluding interface, that provides a first interface ofcontact between the confronting surfaces of the stator and rotor in theevent the rotor moves axially toward the stator during dynamic operationof the seal.
 8. The labyrinth seal according to claim 2, wherein thestator includes an annular shoulder rearward of the outermost,radially-extending projection that defines an annular channel, whereinthe annular channel is defined between the annular radially-extendingprojection and a housing, and assists in running off of a contaminantliquid away from an entrance into the labyrinth seal when the stator isinserted axially into a receiving bore of the housing.
 9. The labyrinthseal according to claim 1, wherein the confronting surfaces of thestator and rotor further define a radially-inside exclusion chamberdefined in part by the first radially-extending annular surface of therotor and an annular intermediate projection of the stator disposedradially inwardly from the intermediate projection of the rotor.
 10. Thelabyrinth seal according to claim 2, wherein the radially-outermostannular interface passage tapers radially outwardly and axiallyrearwardly at an acute angle relative to an axial reference line. 11.The labyrinth seal according to claim 1, wherein the axial width of theradially outside exclusion chamber is greater than the axial thicknessof the annular rearwardly-extending, radially-inboard intermediateprojection of the rotor, by the width of a second radial interfacepassage between a distal end of the annular rearwardly-extending,radially-inboard intermediate projection of the rotor and the firstradially-extending annular surface of the stator.
 12. The labyrinth sealaccording to claim 11, further having a radially-outermost annularinterface passage between an annular, outermost, radially-extendingprojection of the stator and the annular rearwardly-extending distalprojection of the rotor that includes an annular inner surface thatfaces radially inwardly and overlaps the outermost, radially-extendingprojection of the stator.
 13. The labyrinth seal according to claim 11,wherein the confronting surfaces of the stator and rotor further definea radially-inside exclusion chamber defined in part by the firstradially-extending annular surface of the rotor and an annularintermediate projection of the stator disposed radially inwardly fromthe intermediate projection of the rotor.
 14. The labyrinth sealaccording to claim 13, wherein a virtual radial plane perpendicular toan axial reference line passes through a portion of both theradially-outside exclusion chamber and the radially-inside exclusionchamber.
 15. The labyrinth seal according to claim 10, wherein theradially-outermost annular interface passage is at an acute angle of atleast 2° , and up to 15° , relative to an axial reference line.
 16. Thelabyrinth seal according to claim 9, wherein a virtual radial planeperpendicular to an axial reference line passes through a portion ofboth the radially-outside exclusion chamber and the radially-insideexclusion chamber.
 17. The labyrinth seal according to claim 9, whereinthe two radially-disposed exclusion chambers are in fluid communicationwith a drain in a bottom of the stator.